In recent times, with the increasing development of information communication technologies and the widespread use of a variety of multimedia services, high-quality communication services are being developed and introduced to the market, and the demand of users who desire to use the high-quality communication services is being abruptly increased.
In order to actively cope with the increasing demand of the users, capacity of a communication system must be increased. Basically, available frequency resources are limited under wireless communication environments. In order to increase communication capacity under the wireless communication environments, there is a need to more effectively use an available frequency band.
In order to increase efficiency of radio resources, a variety of communication methods for use of STC (Space Time Code) or spatial multiplexing (SM) techniques have been proposed.
In more detail, the above-mentioned STC communication method mounts a plurality of antennas to a transmission/reception unit to additional guarantee a spatial area for utilization of resources, such that it can increase reliability of a communication link via a diversity gain without increasing a bandwidth. The above-mentioned SM communication method performs parallel transmission of data, such that it can increase data transmission capacity.
Besides, a Full Diversity Full Rate Space Time Code (FDFR-STC) technique for simultaneously acquiring a multiplexing gain and a spatial multiplexing gain has been recently proposed.
FIG. 1 is a block diagram illustrating a transmitter having a multi-antenna.
Referring to FIG. 1, the transmitter includes a channel encoder 11, a mapper 12, a serial/parallel converter 13, and a multi-antenna encoder 14.
The channel encoder 11 performs the channel encoding of an input data bit according to a predetermined algorithm. The channel encoding process adds a redundancy bit to the input data bit, such that it can generate a robust signal which has very strong resistance to noise. The mapper 12 performs the constellation mapping of the channel-encoded bit, and converts the mapped bit into a symbol. The serial/parallel converter 13 converts the serial symbol generated from the mapper 12 into a parallel symbol, such that the symbol generated from the mapper 12 can be transmitted via a multi-antenna. The multi-antenna encoder 14 converts the parallel channel symbols into a multi-antenna symbol.
FIG. 2 is a block diagram illustrating a receiver equipped with a multi-antenna.
Referring to FIG. 2, the receiver includes a multi-antenna encoder 21, a parallel/serial converter 22, a demapper 23, and a channel decoder 24. The multi-antenna encoder 21 receives the multi-antenna symbol, and converts the received multi-antenna symbol into a channel symbol. The parallel/serial converter 22 converts the parallel channel symbols into serial channel symbol. The demapper 23 performs the constellation demapping of the serial channel symbol. The channel decoder 24 decodes the bits received from the demapper 23.
If the multi-antenna encoding is performed as described above, a multi-antenna gain is changed according to the encoding methods. Therefore, a Full Diversity-Full Rate Space Time Coding (FDF-STC) is required to acquire an optimum performance.
Data transmission capacity of the wireless communication system can be considerably increased using the above-mentioned Multiple-Input Multiple-Output (MIMO) technology.
A representative conventional art of the MIMO technology has been proposed by Alamouti, entitled “A SIMPLE TRANSMIT DIVERSITY TECHNIQUE FOR WIRELESS COMMUNICATIONS”, IEEE JSAC, vol. 16. No. 8, October 1998, which is incorporated herein by reference. The above-mentioned conventional art of Alamouti relates to a Transmit Diversity technique for obviating the fading of RF channels using a plurality of antennas contained in the transmission/reception unit. The above-mentioned conventional art of Alamouti is indicative of a method for transmitting data via two transmission antennas, has a diversity order corresponding to the product of the number of transmission antennas and the number of reception antennas, such that it can acquire a maximum diversity gain (also called a “full diversity gain”).
However, the above-mentioned conventional art of Alamouti has been designed to transmit only two data symbols during two time slots via two transmission antennas, such that a transmission rate of 1 is acquired. As a result, the conventional art of Alamouti cannot acquire a spatial multiplexing gain irrespective of the number of reception antennas. The conventional art of Alamouti has not proposed a data transmission method for a specific case when three or more transmission antennas are used.
In the meantime, a representative example for acquiring a spatial multiplexing (SM) gain is a Vertical Bell Laboratories Layered Space-Time (V-BLAST) method, entitled “DETECTION ALGORITHM AND INITIAL LABORATORY RESULTS USING V-BLAST SPACE-TIME COMMUNICATION ARCHITECTURE”, IEEE, Vol. 35, No. 1, pp. 14˜16, 1999.
According to the above-mentioned example for acquiring the SM gain, a transmitter simultaneously transmits different signals of individual transmission antennas at the same transmission power and the same transmission rate. A receiver detects the signal of the transmitter using three methods, i.e., a detection ordering method, an interference nulling method, and an interference cancellation method, etc., such that it removes an unnecessary interference signal from the received signal, resulting in the increased SNR.
The above-mentioned conventional method for acquiring the SM gain can simultaneously transmit separate data signals equal to the number of transmission antennas on the assumption that the number of reception antennas is equal to the number of transmission antennas, such that the spatial multiplexing (SM) gain can be maintained at a maximum value.
However, the above-mentioned conventional method has a disadvantage in that the number of reception antennas should be higher than the number of transmission antennas. In order to maximize the multiplexing gain, the diversity gain cannot be acquired at the diversity order of 1. If a signal is wrongly recovered under the poor channel environment, the wrongly-recovered signal may unavoidably affect the next transmission signal, resulting in the deterioration of performance.
In the meantime, a representative example of a titled-QAM scheme has been introduced in Globecom conference, entitled “STRUCTURED SPACE-TIME BLOCK CODES WITH OPTIMAL DIVERSITY-MULTIPLEXING TRADEOFF AND MINIMUM DELAY”, pp. 1941˜1945, 2003, which is hereby incorporated by reference.
The above-mentioned tilted-QAM scheme of the Globecom conference relates to the STC code for acquiring a Full Diversity & Full Rate (FDFR) capable of satisfying an optimum diversity-multiplexing tradeoff scheme. The above-mentioned tilted-QAM scheme employs a short space-time block code having a minimum code length of 2, when two transmission antennas and two reception antennas are used.
However, the above-mentioned tilted-QAM scheme cannot sufficiently acquire a coding gain, and configures a code using the combination of several data symbols, such that it has a disadvantage in that an encoding complexity unavoiably increases.
In conclusion, there must be newly developed a new space-time code (STC), which has higher efficiency and lower encoding complexity in consideration of diversity and coding gain.